1. Field of the Invention
The present invention relates to a colored curable composition favorably used in producing a color filter for use in liquid crystal display elements and solid state image pickup elements, a color filter prepared by using the colored curable composition, and a method of producing the same.
2. Description of the Related Art
Color filters having yellow, magenta, and cyan filter layers and color filters having red, green, and blue filter layers formed together on the same surface of a substrate have been known as the color filters formed for color development on various elements such as solid state image pickup element and liquid crystal display element. A belt-shaped or mosaic pattern is formed with the filter layer in such a color filter.
Various preparative methods were proposed for production of such a color filter. Among them, a so-called color resist method of forming a pattern by exposure and subsequent development of a photosensitive resin composition containing a dye repeatedly for particular times has been practiced widely commercially.
The color resist method, which is a method of preparing a color filter by photolithography by using a colored radiation-sensitive composition containing a pigment dispersed in a photosensitive composition, is considered to be suitable for production of a color filter for large-screen high-resolution color displays, because the color filter is resistant, for example, to heat and light because a pigment is used and also superior in positional accuracy because of the patterning by photolithography.
When a color filter is prepared by a pigment dispersion method of dispersing a pigment as described above, the color filter is prepared by repeating the procedures of coating a radiation-sensitive composition on a glass plate, for example by using a spin coater or a roll coater and obtaining a colored pixel by pattern exposure and development of the coated film, according to the desirable number of colors. Disclosed are many negative working photosensitive compositions containing a photopolymerizable monomer and a photopolymerization initiator together with an alkali-soluble resin that are used in the pigment dispersion method (see, for example, JP-A Nos. 1-102,469, 1-152,499, 2-181,704, 2-199,403, 4-76,062, 5-273,411, 6-184,482, 7-140,654, and 2002-14,222).
However, there is a demand recently for improvement in the resolution of the color filter for use in solid state image pickup elements. However, conventional pigment dispersion systems described above, which were not satisfactory in resolution and had a problem of unevenness in color caused by bulky pigment particles therein, were not suitable for applications demanding fine patterning such as solid state image pickup element.
To overcome the problems, use of a traditional dye was proposed (see, for example, JP-A Nos. 6-75,375 and 2002-14,221 and JP-B No. 7-111,485). However, such dye-containing curable compositions also had the following problems and demanded further improvement thereon:
(1) Dyes are generally lower in heat resistance and light stability and also in fastness than pigments.
(2) When the molar absorption coefficient of a dye is low, it is needed to add a greater amount of the dye, and in such a case, it is necessary to reduce relatively the content of the other components in curable composition, such as polymerizable compound, binder, and photopolymerization initiator, which leads, for example, to deterioration in the curable efficiency of the composition, the heat resistance of hardened region, and the developing efficiency of unhardened area.
(3) Such a dye often interacts with the other components in the curable composition, making it difficult to control the developing efficiency (solubility) of the hardened and unhardened regions.
Thus, the dyes used in traditional photosensitive compositions were unsatisfactory especially in fastness and also lower in solubility in the photosensitive composition, often leading to precipitation of the dye in the liquid or coated-film state and thus, prohibiting addition of the dye at higher concentration.
On the other hand, a mixture of violet and cyan dyes is known to be used for the blue filter array of color filter (see, for example, JP-A No. 2002-14,222). However, the dyes used in JP-A No. 2002-14,222 were unsatisfactory in heat resistance and light stability and thus demanded further improvement.
As described above, although dye-containing curable compositions are useful in applications demanding high resolution and uniform color such as solid state image pickup element, the stability in the color density and tone of the dye, for example against discoloration, is still unsatisfactory, and there is a concern about the fastness, such as heat resistance and light stability, especially of cyan and violet dyes. There is also a demand for improvement in the resistance to dye precipitation due to the low stability over time thereof in the state of liquid preparation or coated film, because the dyes are less soluble. There was also a concern about the color remaining in the unexposed region in the step of forming a pattern by exposing and developing the dye-containing photosensitive resin composition.